Some existing expanding plugs are made of elastic material and are forced into the aperture which is to be closed, the plug being held by the radial forces exerted on the walls of the aperture. Devices of this kind have the disadvantage of requiring materials which have poor resistance to temperature and which age rapidly. In addition, plugs of this kind are difficult to fit in position, because they require complicated applicances to exert the considerable forces needed for inserting the plug inside the aperture.
Other plugs comprise mechanical arrahgements passing from one side to the other of the aperture which is to be closed, and requiring manual intervention from both sides of the wall in which the aperture is provided; intervention from both sides of the wall is not always possible. Moreover, it is difficult to design a system for the fitting of such plugs with the aid of a remote control apparatus because of the large number of operations required for putting the plug in position.
Other expanding plugs are provided with fastening means acting solely by friction. Devices of this kind are generally not very reliable, because their maintenance in the aperture depends on the coefficient of friction of the parts in contact with the walls of the aperture. This coefficient of friction may however vary, for example in accordance with variations of temperature, vibrations or the presence of fluid. Slippage is therefore always possible.
Other plugs are also known, for instance as disclosed by U.S. Pat. No. 3,267,793, in which a gripping member can be inserted inside the aperture and protrudes on the other side of the wall, and in which a screw means permits expansion of the elastic protruding parts of the member so that they can get a support on the inaccessible rear side of the wall. But in such plugs some parts of the gripping members must be less resistant to allow their expansion, and breakage could occur, especially in case of greai variations of temperature or of vibrations.
French Pat. Nos. 1,211,818 and 1,343,577 disclose plugs with gripping means for locking a plug in a duct, where gripping members are articulated on the plug and liable to be expanded by rotating around their axles so that their other ends will protrude beyond the external surface of the plug. Such mechanisms are somewhat expensive, owing to their articulations. Furthermore, and especially for plugs of low diameter, axles are brittle pieces liable to breakage. Breakage of such element can lead to the presence of uncontrolled free metallic pieces on the inaccessible side of the wall, and to serious damage to the installation.
The present invention consequently relates to an expanding plug which does not have the disadvantages mentioned above. This expanding plug is able to be fitted in position by extremely simple manipulations which can be carried out at a distance by remote-controlled apparatus. This plug is also able to be placed in position by intervention on only one side of the wall, and includes no brittle parts.